2.15 - 2.17 (movements of substances in and out of cells)

Question 1

what is the diffusion theory

Answer 1

diffusion is the movement of molecules from a region of high concentration to a region of low concentration

Question 2

what does diffusion help with

Answer 2

• obtaining many of organism’s requirements
• getting rid of waste products
• carrying out gas exchange for respiration

Question 3

is diffusion an active or passive process

Answer 3

it is passive

Question 4

what is the osmosis theory

Answer 4

osmosis is the movement of water form a region of higher water potential to a region of lower water potential through a partially permeable membrane

Question 5

what happens if an animal cell is placed into a solution with a lower water potential than the cell?

Answer 5

it will lose water by osmosis and become crenated (shrivelled up)

Question 6

what happens if an animal cell is placed in a solution with a higher water potential than the cell?

Answer 6

the water will keep moving into the cell by osmosis and the cell may burst

Question 7

what happens if a plant cell is placed in a solution with a lower water potential than the cell?

Answer 7

the cell will get smaller as a result of lost water and the vacuole will get smaller which makes the cell membrane shrivell away from the cell wall
- it is flaccid or plasmolysed

Question 8

what happens if a plant cell is placed in a solution with a higher water potential than the cell?

Answer 8

the vacuole gets bigger and it will push the cell membrane against the cell wall
- it is turgid

Question 9

what is active transport theory

Answer 9

the movement of particles through a cell membrane from a region with lower concentration to a region with higher concentration using energy from respiration

Question 10

what is it “active” transport

Answer 10

because it requires energy as the particles are moving against a concentration gradient (it is the opposite of diffusion)

Question 11

what does active transport allow glucose to do?

Answer 11

it allows glucose to be transported into the bloodstream even when the concentration of sugar molecules in the blood is higher

Question 12

what does active transport allow root hair cells to obtain?

Answer 12

root hair cells need to move minerals such as magnesium ions from a region with a low concentration to a region of high concentration
so it allows root hair cells to transport minerals from the soil into the cytoplasm of the cell.

Question 13

why are mineral ions needed to make a plant function

Answer 13

magnesium ions are required to make chlorophyll and nitrate ions are needed to make amino acids for protein synthesis

Question 14

how does surface area to volume ratio influence diffusion?

Answer 14

the bigger the cell is, the smaller its surface area to volume ratio is which slows down the rate of diffusion

Question 15

how does diffusion distance affect the rate of diffusion

Answer 15

the smaller the distance, the faster active transport will occur

Question 16

how does temperature affect the rate of diffusion

Answer 16

the higher the temp. the faster the molecules can move (more energy)
so a faster rate of diffusion

Question 17

how does concentration gradient affect the rate of diffusion

Answer 17

the greater the difference in concentration the faster movement will occur

Question 18

practical: factors that influence diffusion
how can we investigate how temp. affects diffusion rate?

Answer 18

using beetroot.
if it is heated above 45°c it can damage the cell membrane and the pigment can leak out
the speed of the pigment leaking out of the cell tells us about the rate of diffusion

Question 19

practical: factors that influence diffusion
how do you carry out this practical?

Answer 19

1.use a knife to cut equally sized cubes of beetroot
- they need to be equal to have the same volume to SA ratio
2. rinse the beetroot pieces to remove any pigment that leaked from the cutting
3. put 5 cm^3 of water into 2 test tubes labelled A, B
4. keep test tube A at room temp
and keep test tube B at 90°c
5. leave the test tubes for 2 minutes then add the beetroot pieces in them
6. after 10 mins observe the colour of the liquid in both test tubes

Question 20

practical: factors that influence diffusion
why did more pigment leak out of the hotter temperature?

Answer 20

the cell membrane of the betroot cells were damaged so more pigment was able to leak out
and at a higher temperature the particles have more kinetic energy so they had faster movements compared to when they had less heat (energy)

Question 21

practical: factors that influence diffusion
what could be improved in this practical?

Answer 21

• the beetroot sizes have to be identical so use a ruler and a knife and repeat the investigation to have an average
• some parts of the beetroot could have had more pigment so to fix this more repeats could be taken with different parts of the beetroot
• instead of testing 2 temperatures, a range of temperatures could be tested.
• lastly, using a colorimeter can help be more accurate instead of just observing the color difference with our bare eyes.

Question 22

practical: factors that influence osmosis
what do we use to investigate osmosis

Answer 22

potato cylinders in distilled water and sucrose solutions of increasing concentrations

Question 23

practical: factors that influence osmosis
how do we carry out this practical?

Answer 23

1. prepare a range of sugar solutions from distilled water to a very high concentration of sugar solution
2. set up 6 labelled test tubes yith 10cm^3 of each of the sucrose solutions
3. cut 6 equal potato cylinders
4. dry each one (blot) and weigh them
5. put one piece in each test tube
6. after 4 hours, remove them, blot them with paper towel, and weigh them
7. calculate the difference in the original and new weight and calculate the % change in mass.
8. to do this you use the formula
   final mass-initial mass /initial mass x 100

Question 24

practical: factors that influence osmosis
what could be improved?

Answer 24

• the cylinders need to be exact to fix this, we could do multiple trials in order to calculate a mean without any anomaly.